Betapack 1 flicker - check your nuts!

[kgallen]

I recently had an issue with one of our Betapack 1's where there was some instability/flicker on channels 3 and 4.

Tonight I've tracked that down to loose nuts on the mains inlet - not the ones on top of the phase joining bar, but the ones *underneath* that clamp the M6 bolts to the metal phase plates on the PCB. You will only find this by removing the phase joining bar which otherwise holds the three bolts locked together (assuming the top nuts are tight which are the easy ones to check!). Pair of 10mm spanners to tighten. Check all three phases and the neutral too, as whilst phase 2 was distinctly loose on mine, phase 3 and the neutral also needed a tweak. There should be spring washers in place too under the nuts.

Diagnosed by having some lamps plugged in and tapping around the case with the rubber handle end of a screwdriver and seeing some flicker and hearing a little buzzing/crackling every now and again!

Recording for the reference of others competent to remove the rear panel - danger, mains voltages, unplug/isolate before doing so!